1. Field of the Invention
The present invention relates to a polarization device employed in a polarization illumination system for a liquid crystal light valve which is used in a projection type display apparatus, and a projection type display apparatus that projects modulated light emitted from the light valve illuminated by a polarization illumination system employing the polarization device on a screen as an image.
2. Description of the Related Art
An illumination system employing two lens plates, i.e., the so-called fly-eye lens plates, is used in a method for evenly illuminating a rectangular illumination area such as a liquid crystal light valve or the like in the known art.
In addition, a polarization illumination system, which improves the illuminating efficiency in the illumination system described above by disposing a polarization beam splitter array and halfwave plates at a specific position at the emission surface of the second lens plate of the two lens plates to improve the utilization efficiency of the light source light, and a projection type display apparatus employing this illumination system have been proposed (see Japan Laid-Open Patent Publication No. 8-304739 (PCT international publication No. WO 96/20422)).
FIG. 18 in this specification presents FIG. 8 in the above mentioned publication, which was used to explain the polarization device and the projection type display apparatus given as an example of a variation of the fifth embodiment in the publication.
In the example of the prior art in FIG. 18, a light source unit 102 comprises a light source lamp 100 and a parabolic reflector 101 constituted of a concave mirror such as a parabolic mirror, and beams emitted from the light source unit 102, which are almost parallel to one another, enter a first lens plate 104 constituted by providing a plurality of lenses 103 in a planar configuration. The light emitted from the first lens plate 104 enters a plurality of lenses 106 constituting a second lens plate 105. During this process, since the individual lenses 106 of the second lens plate 105 are formed in conformance to the shape of the lenses 103 of the first lens plate 104 and are provided at the focal points of the lenses 103, the light from the individual lenses 103 of the first lens plate 104 converges at the lenses 106 of the second lens plate 105.
In addition, a polarization beam splitter array (hereafter referred to as a PBS array) 108 comprising a plurality of polarization beam splitters (hereafter referred to as PBS's) 107 is provided at the emission surface of the second lens plate 105, and a halfwave plate 109 is provided at every other PBS 107 at the emission surface of the PBS array 108. Furthermore, a condenser lens 110 is provided on the side where the emission surfaces of the halfwave plates 109 are present.
In the figure, the roughly parallel beams that have entered the lenses 103 of the first lens plate 104 are converged in the approximately central areas of the lenses 106 constituting the second lens plate 105, as described above, then are emitted from the lenses 106 to enter the PBS's 107 constituting the PBS array 108 and are transmitted through polarization splitter portions 107a provided diagonally at the PBS's 107 to undergo the process of polarization splitting in which the light is divided into p-polarized light that is directly emitted and s-polarized light that is reflected by the polarization splitter portions 107a of the PBS's 107 to enter adjacent PBS's 107. The s-polarized light entering the adjacent PBS's 107 is then reflected by the polarization splitter portions 107a of the PBS's 107 and is emitted in the direction matching that of the optical axis of the light that entered the lenses 106.
With the halfwave plates 109 provided at the emission surfaces of the PBS's 107 where the p-polarized light is emitted and the p-polarized light entering the halfwave plates 109 is converted to s-polarized light for emission. As a result, all the light from the light source that has entered the lens plates is emitted as s-polarized light.
The s-polarized light travels through the condenser lens 110 and then enters a light valve 111 to illuminate the light valve 111 with a high degree of efficiency.
It is clear that by adopting this structure, which is provided with the PBS array 108, the halfwave plates 109 and the like, lighting with a far higher degree of intensity is achieved in polarized illumination of the light valve 111 with the s-polarized light compared to an illumination system employing only the first lens plate 104 and the second lens plate 105.
In other words, in the method that only employs the first lens plate 104 and the second lens plate 105, and not the PBS array 108, since random light illuminates the light valve 111, only linearly polarized light in one direction in the random light is used as incident light entering the light valve 111.
However, the need for achieving a higher degree of intensity for projected images on projection type display apparatuses has been growing with ever increasing urgency in recent years.
In this regard, polarization illumination systems employing the prior art method are by no means satisfactory, as detailed later, and the inventor of the present invention et al. have conducted research by regarding such a polarization illumination system as an integrated polarization device which includes a light source unit, and observed that the original functions of the polarization device are not wholly fulfilled.